Colour printing



June 17, 1969 w. M. DIXON 3,450,044

COLOUR PRINTING Filed May 20, 1966 United States Patent US. Cl. 101-470 6 Claims ABSTRACT OF THE DISCLOSURE A method of colour printing upon sheet material comprises subjecting the material to a first printing operation, whereby it is printed on one side with a first overall pattern comprising rows of closely spaced substantially square-shaped and wholly inked areas, and thereafter subjecting said one side of the material to a second printing operation, whereby the first over-all pattern is overprinted with at least a second overall pattern substantially identical in configuration, size and colour to the first overall pattern but angularly disposed in relation thereto. Preferably, the square-shaped areas are spaced from each other by a distance of from one-eighth to one-quarter of the side of said square-shaped areas.

This invention relates to colour printing and in particular to a process for producing printed sheets and webs which have a uniform overall tone dispersion when viewed at an average viewing distance. The invention concerns more particularly the production of decorative print sheets for use in the manufacture of decorative laminated plastics board but it is by no means limited to this single application.

Known decorative sheet materials, having uniform or substantially uniform overall tonal effects, exists in a variety of forms; for example, self-coloured sheets, especially sheets of paper incorporating pigments added at the time of manufacture of the paper, are widely used for artistic purposes including the creation of single colour decorative surfaces in laminated plastics boards. However, when such decorative sheet materials are required to be available in a very large number of different colours, as is inevitably the case when the products are to be used for internal and external decoration, the use of pigment-loaded papers is not an economically attractive proposition, because, for every one of the large number of colours required and even for slight changes in shade, it is necessary to make a special batch of papers; the pigments are expensive and, in order to buy at a good price, it is necessary to purchase in large quantities for every colour and shade and to find the necessary storage space for paper which may not be needed for some considerable time.

It is also known to obtain the desired effect by coating the required colour onto paper having either a white or pigmented surface; it is thus possible, especially by the use of paper having a pigmented surface, to obtain a wide variety of tonal elfects, but, for mass-production purposes, this method suffers from the disadvantages that it is difiicult to coat large areas of unbroken colour whilst maintaining exact colour consistency, particularly from one batch to the next.

One object of this invention is to produce Web or sheet materials each having virtually any desired uniform overall tonal value when viewed from an average viewing distance and which may thus for all practical purposes be regarded as a plain colour, without it being necessary to employ anything more than a very small fraction of the number of separately coloured web or sheet materials that would be necessary to obtain results by the use of previously known methods.

A second object of the invention is to provide web or sheet material with a uniform overall tonal value when viewed from an average viewing distance by the application thereto of two or more superimposed printed patterns of such a nature that no specific degree of register is required therebetween and that the problems associated with the undesirable moir elfect do not thus arise.

According to this invention, a method of colour printing upon web or sheet material consists in subjecting the material to a first operation, in which it is printed with a first overall pattern comprising rows of spaced substantially square-shaped inked areas, and thereafter subjecting the material to at least a second operation, whereby the first overall pattern is overprinted with at least a second overall pattern substantially identical in configuration, size and colour to the first overall pattern but angularly disposed in relation thereto.

In cases where more than one overall pattern is printed over the first, the angular disposition of each of them to first pattern i preferably different.

The surface of the web or sheet before the printing operations may be white or coloured; preferably, however, the surface colour ranges from white through tonal values of grey to black. The ink used for the printing operations preferably differs in colour or shade from the surface colour of the web or sheet.

The printing operations are preferably carried out by the use of printing cylinders, the printing surfaces of which are continuous, that is to say, they are of such a nature that no join is discernable at any point on the surface of the cylinder, thereby permitting unbroken printing therefrom upon web materials of indeterminate length. The square printing zones on the cylinders are preferably intagliated, each such zone comprising a matrix of closely abutting, substantially square-shaped ink retaining cells. Conveniently, the individual cells are produced mechanically by the use of an embossing tool which, in the production of the cylinder, is adapted for incremental advancement longitudinally and circumferentially in relation to the surface of the printing cylinder.

In order to obtain the best results there are between ten and thirty substantially square-shaped inked areas per linear inch, with a spacing between adjacent such areas of between one eighth and one quarter of the side length of each inked area. A particularly satisfactory effect is obtained when there are fourteen squares per linear inch with spacings equal to one fifth of the side length of the squares.

Although overprinting with two or more identical patterns is within the scope of the invention, we have found that particularly good results are obtained with a single overprinting at an angle of between 40 and 50, and more especially at 45 to the first printing.

We have found that it is not necessary to be dependent upon the incorporation of pigments into paper at the time of manufacture or the colour coating of the surface of paper in order to obtain any particular overall desired decorative effect. By means of this invention, virtually any desired overall colour effect can be obtained by choosing, as raw material, paper having one of a limited number of surface colours, produced by either of the aforementioned known methods, and printing thereupon two or more superimposed patterns of a certain type and with inks of the same colour for each pattern, the inks themselves being prepared by suitable selection and mixing of inks of a limited range of colours. Dependent upon the colours and intensity of the paper and of the inks used,

the printed pattern is visible in the finished product to a greater or lesser extent, but, in any event, the processes described in this specification result in the production of decorative sheet material having a desired uniform overall tonal value when viewed at an average viewing distance; by this we mean a distance of, for example, five to eight feet.

For all practical purposes, the implementation of this invention requires the manufacture of web or sheet materials having coloured surfaces ranging from white through tonal values of grey to black, thus obviating the need for such materials to be produced with the exact shade or colour which is required in the finished product. Similarly, the invention requires the use of a coloured ink, in conjunction with the surface colour of the web or sheet, formulated from or comprising one or more of the three basic colours, black and white; for example, we have found that almost any desired colour effect can be obtained, using webs or sheets having the colours and shades mentioned above, from inks compounded from one or more of the following:

White (e.g., Kronos White) Yellow (e.g., Cadmium Yellow) Red-yellow (e.g., Cinquasia Red) Red-blue (e.g., Cadmium Red) Blue-yellow (e.g., Heliogen Blue) Blue-red (e.g., Cobalt Blue) Black (e.g., Bayer Black) The inks employed are preferably sufliciently opaque for brilliant colours to be obtained, but are sufficiently translucent for a visual distinction to be seen between those areas which are overprinted and those which are not. The pattern prominence or contrast differs in accordance with the difference in tonal contrast between the ink colour and the background colour and essentially nonpatterned colour effects are obtained when the orthochromatic tonal values of the coloured ink and the background are substantially equal.

The invention lends itself readily to the mass production of printed web material of indeterminate length, because no specific register or coincidence of pattern is required between the first, second and, if used, subsequent printed impressions. No matter where each printing operation starts and finishes, the overall effect is the same and the moir effect cannot occur; this results from the maintenance of angular displacement between one printing and the next and the fact that, between points of near coincidence (that is where the pitch centres of the superimposed angularly disposed squares are in apparent coincidence), the overprinted patterns are progressively tending two dimensionally either towards or away from conditions where such coincidence obtains. Theoretically, however, in the case where there are two printings, one at 45 to the other, there is no such exact coincidence because, with constant spacing between the squares, no multiplier will make the square root of 2 (i.e., the width of the diamond) a whole number.

The inks used in the production of laminate print sheets are necessarily resin based; they preferably include melamine-formaldehyde resins, but epoxy or urea-formaldehyde resins may alternatively be employed. Such inks must, furthermore, be colourfast and physically stable in a general sense and the pigments, which must be used in order to produce satisfactory results, give rise, in conjunction with the resinous vehicles, to the formulation of relatively viscous inks. Furthermore, good ink transference and coverage is required in laminate print sheets and we have found that the best results on paper are obtained by the use of an intaglio printing process.

Although this invention has a ready application in the decoration of paper materials, it may also be used in conjunction with base materials of other types, e.g., fibrous sheets and webs of other kinds and metallic foils.

An example of the invention will now be described by reference to the accompanying drawing, in which:

FIGURES 1 and 2 are representations of two separate impressions applied to a sheet of paper, and

FIGURE 3 shows the combined superimposed impressions of FIGURES 1 and 2.

All three figures are to the same scale and include corresponding fragmental portions which show the structure of the printing modules in detail, other portions being drawn in broken lines to illustrate the skeleton outline.

Two copper surfaced steel printing cylinders of 30 inch circtunference were prepared with a multiplicity of square modules having a pitch of 14 per linear inch and a spacing therebetween equal to one fifth of the side length of the modules. In the illustrations, the modules have been cross-hatched for clarity reasons, but each actually comprises a multicellular structure of twenty-five closely abutting square ink retaining cells each capable of retaining ink in accordance with the well known intaglio printing techniques. Each module was produced by means of a multiple embossing tool, which was incrementally traversed around the circumference and length of the surface of the copper surfaced cylinder in such a manner as to produce the twenty-five cell units simultaneously. The spacing of the modules was carried out by well known techniques, which included the use of a dividing head to position the cylinder in the desired angular position relative to the embossing tool and a traversing screw capable of acurately sitting the tool longitudinally in equal incremental positions along the cylinder.

FIGURE 1 shows a first print in which the square inked areas have been printed from a cylinder with its modules normal to the cylinder axis and FIGURE 2 shows a second print in which the square inked areas have been printed from a second cylinder with its modules at 45 to those on the first cylinder. From the combined superimposed printing, shown in FIGURE 3, it can be seen that, because angularly disposed identical squareshaped printing modules were used, any repeat or more correctly near repeat, of the overall pattern occurs at very infrequent intervals. However, the overall tonal effect is substantially constant, but, on close examination, the finished print can be seen to possess minute sparsely distributed unprinted zones in which the background only is visible, other zones, where one of either inked impressions only is visible on the background, and other zones when both are present in a superimposed manner. It can thus be appreciated that, by the suitabe selection of background and colour impressions, an extremely wide range of tonal effects may be readily produced. It is quite possible to emphasise the texture of the pattern by the selection of suitable colour combination, or, alternatively, the selection may be such that an apparent overall colour effect, in which the pattern is barely visible, is obtained.

In one specific example, a light grey surface coloured paper was subjected to the two printing operations described above with reference to FIGURES 1 and 2. The ink used was compounded from mixtures of equal parts of a cobalt blue ink and a cadmium yellow ink (both being melamine-formaldehyde resin based) and the overall effect of the two printings corresponded to the result indicated in FIGURE 3. The resultant green effect was delicately flecked with small grey areas but, when viewed from a distance of six feet, appeared as an overall subtle tone of green.

The modular size and pitch of the printed areas may be either larger or smaller than as described above to suit a wide variety of resolution requirements; for example, rollers having twenty-eight modules to the linear inch may be used. Furthermore, if desired, adjacent rows of the square modules may be ofiset in such a manner that the nonprinting zones define continuous straight lines in one direction only.

What is claimed is:

1. A method of colour printing upon sheet material to provide a decorative sheet material having a substantially uniform overall tonal value and being free from moire cha-racter, said method consisting in subjecting the sheet material to a first operation, whereby it is printed on one side with a first overall pattern comprising rows of substantially square-shaped and-wholly inked areas spaced from each other by a distance not exceeding one quarter of the side of said square-shaped areas, and thereafter subjecting said one side of the material to at least a second operation, whereby the first overall pattern is overprinted with at least a second overall pattern substantially identical in configuration, size, spacing and colour to the first overall pattern but angularly disposed in relation thereto.

2. A method of colour printing as claimed in claim 1 consisting in subjecting the material to more than two operations, the angular dispositions of the subsequent overall patterns being different one from another and from that of the first overall pattern, said subsequent patterns being substantially identical in configuration, size, spacing and colour to the first overall pattern.

3. A method of colour printing as claimed in claim 1 in which the sheet material has a coloured surface and the ink used in the printing operations is of a colour different from that of said coloured surface.

4. A method of colour printing as claimed in claim 2 in which the overall patterns comprise between ten and thirty substantially square-shaped inked areas per linear inch with a spacing between adjacent such areas of between one-eighth and one-quarter of the side length' of each inked area.

5. A method of colour printing upon sheet material according to claim 1 wherein both said first and second operations are intaglio printing operations, and wherein said second overall pattern is at an angle of between 40 and 50 to said first overall pattern.

6. A method of colour printing as claimed in claim 5 in which the second pattern is at an angle of to the first pattern.

References Cited UNITED STATES PATENTS 2,292,569 8/1942 King 101-211 2,380,047 7/ 1945 Hyman 117-45 2,506,153 5/1950 Hurley 117-38 X DAVID KLEIN, Primary Examiner.

US. Cl. X.R. 

